Protein and Muscle After 40

The protein conversation has two halves, and most coverage runs only one of them.

The first half is real physiology: older muscle responds less readily to protein, and the dose required to overcome that is measurably higher. The second half is a body of randomized trials in which giving older adults more protein produced surprisingly modest results.

Both are true. Holding them together is the point of this article.

Anabolic resistance is real and quantified

When you eat protein, muscle protein synthesis rises for a few hours. With age, the same dose produces a smaller response. The field calls this anabolic resistance.

It has been measured. In younger men, approximately 0.24 g/kg body mass of protein in a single meal maximally stimulated muscle protein synthesis — around 20 grams for most people. In older adults, achieving comparable stimulation required approximately 0.40 g/kg (reviewed in Nutrients, 2018, citing Moore et al., J Gerontol A Biol Sci Med Sci, 2015).

That is roughly 68% more protein per meal to produce the same signal.

For an 80 kg person, the arithmetic is straightforward: about 19 g per meal at 30, about 32 g per meal at 70. Most people’s breakfast does not clear the second threshold. Many people’s lunch does not either. The typical Western pattern loads most protein into dinner, which means one adequate stimulus per day rather than three.

The same review notes a ceiling on total intake for training adults. A meta-analysis found that beyond a daily protein intake of 1.6 g/kg/day (95% CI 1.0–2.2), protein supplementation failed to augment resistance-exercise-induced muscle hypertrophy.

So the physiological picture is coherent: older muscle needs a larger per-meal dose, and there is a total daily intake beyond which more stops helping.

The trials are less impressed

Now the second half.

The Health Council of the Netherlands commissioned a systematic review asking a direct question: does protein intake above the current population reference intake improve outcomes in older adults? The findings, published in Advances in Nutrition, are sobering (Hengeveld et al., 2021).

Lean body mass: “possible beneficial effect.” Seven of 18 randomized trials (39%) showed improvement; 21 of 62 tested contrasts (34%) reached significance. Where benefits appeared, effect sizes ranged from 1.2% to 3.7% relative change over 10–12 weeks.

Muscle strength with resistance exercise: “possible beneficial effect.” Three of eight trials with exercise (38%) showed improvement, but only 3 of 24 contrasts reached significance.

Muscle strength without exercise: “likely no effect.” One of seven trials (14%).

Physical performance: “likely no effect.” Two of 12 trials (17%), involving 3 of 44 contrasts (7%).

The committee also flagged quality: half the studies carried high risk of bias and half had some concerns. Their overall verdict was that insufficiently convincing data support substantial health benefits from increased protein in older adults already meeting current intake recommendations.

Extra protein without resistance training is, on this evidence, likely to do nothing for strength or physical function.

That last clause matters. This is not evidence that protein is unimportant. It is evidence that protein is permissive rather than causal — it enables a response to training, and in the absence of training there is little for it to enable.

Why this still matters: what you are defending against

Sarcopenia is not a cosmetic concern. The revised European consensus defines it as a progressive and generalised skeletal muscle disorder associated with heightened risk of falls, fractures, disability and mortality (EWGSOP2, 2019).

The 2019 revision made a significant conceptual change: muscle strength became the primary criterion, with muscle quantity used for confirmation and physical performance indicating severity. Strength, not size.

The diagnostic cut-points are specific and usable:

• Grip strength: below 27 kg for men, below 16 kg for women
• Gait speed: 0.8 m/s or slower indicates severe sarcopenia

Their recommended pathway is Find–Assess–Confirm–Severity: screen with the SARC-F questionnaire or clinical suspicion, assess with grip strength or a chair-stand test, confirm with DXA, BIA, CT or MRI, and stage severity with gait speed or a physical performance battery.

Two of those four steps need no equipment beyond a cheap dynamometer and a tape measure.

Putting the halves together

The coherent reading of this evidence:

Protein is a requirement, not a stimulus. Resistance training is the stimulus. Adequate protein lets you respond to training; inadequate protein caps that response. Excess protein, past roughly 1.6 g/kg/day in training adults, adds nothing measurable.

The per-meal threshold is the part most people get wrong, and it is also the easiest to fix. Distribution matters because muscle protein synthesis responds to individual meals, not to a daily total.

What to do with this

• Aim for roughly 0.4 g/kg of protein per meal if you are over about 50. For an 80 kg person that is about 32 g — a serving of fish, three eggs plus dairy, a large chicken breast, or a well-constructed plant combination.
• Fix breakfast first. It is the meal most likely to fall below threshold, and moving it above threshold adds a full anabolic stimulus to your day at no extra total intake.
• Do not exceed about 1.6 g/kg/day expecting more muscle. The meta-analytic ceiling for training-induced hypertrophy sits there, with a wide confidence interval (1.0–2.2) that argues against precision at the top end.
• Do not supplement protein instead of training. The Dutch review found “likely no effect” on strength without concomitant exercise. Protein without resistance training is the most common and least productive version of this intervention.
• Measure grip strength annually after 50. Below 27 kg (men) or 16 kg (women) is a clinical threshold, not a fitness opinion. A dynamometer costs less than a month of protein powder.
• Time your gait speed occasionally. Walk 4 metres at normal pace. Under 0.8 m/s is a red flag worth taking to a physician.
• If you have kidney disease, discuss intake with your clinician before increasing it. Higher-protein recommendations are made for otherwise healthy older adults.

The framing that survives the evidence is this: protein is the raw material, training is the instruction, and the instruction is the part that is missing from most people’s plan. Buying more raw material to compensate for a missing instruction is the most expensive way to make no progress.